The need to increase the current by the original 21 inch color TV using the STR50213 to increase the power of STR51213, and the addition of the main power supply over current protection circuit.

One, working principle

1 main power supply circuit the main power supply is similar to that of STR5412. D833, R844 and C817 composed of a rectifier and filter circuit, 220V into about 300V voltage pulsation and pipe by internal switch switch T801 of transformer primary winding P1, P2 is added to the IC801 (str51213) Q3 C pole. R803 is the starting resistor, Q3 IC801 for the internal B to provide the starting voltage. F1, F2, F3, T801 for the feedback winding, R804, D805, C806 for the feedback circuit, so that the circuit to maintain the oscillation. R806 and D805 will be sent to the IC801 to make the power oscillation frequency and line scan synchronization. D804 is a continuous flow diode, when the Q3 cutoff, D804 conduction, the energy released from the T801 to improve power efficiency. IC801 internal Q2, D1, Q1 and other components of the voltage regulator circuit, so that the output voltage to remain stable.

Q834 over voltage protection of thyristor with C846, C845 to form the main power over voltage protection circuit. Q802 and R817 to constitute the main power over current protection circuit.

After the main supply and IC801 of 4 feet in the output voltage by C808 filter, line output circuit to the load, providing 113V of DC voltage. S1 T801, S2 winding induction voltage by D801 rectifier, C810 filter, the output 17V DC voltage. The voltage is supplied to the load by 12V and 5V after the 12V and 5V regulator.

2 power circuit the circuit is mainly composed of Q810, D810, Q813 and other components, is a series of DC voltage regulator circuit. Q810 is a regulator regulator, Q813 is the sampling amplifier, D810 is the benchmark regulator. Will be after the main power supply rectifier DC 300V voltage regulator, output is approximately 7V DC voltage and the voltage after standby light emitting diode D813 luminous and buck, and the D814 isolation, C811 filtering, the microprocessor IC1102, reset circuit, and a remote control receiving head to provide approximately 5V DC standby working voltage.

3 the circuit of the switch is closely connected with the auxiliary power supply. Mainly by Q814, Q811 and other components. Boot time, the operation of the secondary power supply, the microprocessor IC1102 provide power, at the same time the DC voltage of approximately 5.3v D814 positive after partial pressure of r813, R814, applied to the power supply control Q811 of the B, the Q811 conduction, the main power supply IC801 control of end of level of a pin is pulled low. IC801 don't play vibration, main power supply output. At the same time, 5V voltage through the power switch on the back of a pair of instantaneous dynamic switching instant, the Q1105 Q1104 instant conduction, the IC1102 pin outputs the key scanning pulse is sent through the feet, and after confirmation IC1102, from 6 feet high level output, after R1150, R1184 partial pressure, the q814 conduction, Q810 base of potential pulled low cutoff, auxiliary power supply stop working, indicator light D813 extinguished, Q811 because B loss of power while the cut-off, rising IC801 fifth pin voltage, main power supply Kai working mode. Send 113V and 17V voltage, in which the voltage regulator circuit 17V and D1118, D1138 to the IC1102 to provide the 5V power supply, for the next power supply.

Remote shutdown, IC1102 6 feet output low level, the q814 cutoff, the operation of the secondary power supply, standby indicator light, Q811 conduction, IC801 oscillation stop, no output voltage.

Composed of an auxiliary power supply over-current protection circuit Q812 R815. When auxiliary power supply due to the current increase to increased to above 0.5V drop R815, Q812 conduction, Q810 forward bias circuit and cut-off, the auxiliary power supply output.

Q851, D851, C870, circuit is composed of 12V circuit. When the 12V load short circuit or for mains failure decrease the output voltage, 12V voltage will decrease, when reduced to below 4V. The C870 delay, Q851 conduction, q814 B pole boot high level is pulled low, q814 cut-off, start the auxiliary power source, Q811 conduction, main power supply stop vibration protection.

Two, troubleshooting

The machine is equipped with a variety of protection circuits. The switch machine circuit is located in the auxiliary power supply, the main auxiliary power supply each other. When the main power failure or action of the protection circuit, the main power supply no output or the output voltage is very low, 12V short circuit owe voltage protection circuit, the auxiliary power supply startup, the indicating lamp is bright and enter the shutdown state protection. When the secondary power failure occurs, the main power supply will be out of control by Q811. Therefore, maintenance, should distinguish the main auxiliary power failure. Approach is to disconnect the R853, so that the connection between the two separate. If you disconnect, the machine can turn on the normal viewing, then the vice power of the fault, should check the auxiliary power supply and switch machine circuit as well as 12V circuit under voltage.

If after disconnecting the R853, machine still does not work or work not normal may be broken open output plug 585, 100W bulb fraud is connected to the load, electricity output voltage measurement; voltage is close to 113V (because at this time there are no sync pulse, the power oscillation frequency is low, output voltage may slightly lower), for the load circuit fault, otherwise for mains failure.

The machine is on standby to indicate whether the light is normal, and it can reflect the working condition of the power supply circuit. Normal, press the power switch, power supply auxiliary work first, standby indicator light, Q811 conduction, the main power supply stops the oscillator, the micro controller to power. Later on, the micro controller, output the starting signal, the auxiliary power source to stop working, standby indicator lights, Q811 deadline, industry and trade of the main power supply as the boot. Therefore, the boot, the standby indicator should be shining, and then put out. When a fault occurs, standby indicator lights will appear in the following situations: (1) always bright and can not boot, the fault coverage may 300V rectifier and filter circuit or an auxiliary power supply circuit. (2) after the light is destroyed, but the three. If accompanied by a "squeak" sound, then the load is slightly short. If there is no "squeak" sound, is the line scanning circuit does not work. (3) bright and not destroyed. It is the fault of the control circuit. (4) after the light is bright, or the shining moment becomes bright. If shining when accompanied by a "squeak" sound, it is loaded with serious fault, cause the main power supply output voltage is too low, 12V undervoltage protection circuit; if there is no "squeak" sound is a mains failure and no output.

To determine the scope of the fault, the maintenance process can be carried out according to the maintenance process.

The following examples of troubleshooting examples, for the reader reference.

[example 1] fault phenomenon on the indicator light is often bright, according to remote control can not boot.

Analysis and maintenance of inspection of key switch control circuit, the foot of the IC1102 0.4 ~ 1.4V high level output, but obviously on the low side, normal should is more than 4V. Check the feet to the various components of no abnormal Q814. Suspect that the action of the Q851 protection circuit, the C pole of the Q851 is broken, and the whole machine is returned to normal. Check Q851 and peripheral elements and found that the C870 capacity decreases, without delay, the foot IC1102 boot high level just one output, Q851 breakover. When the main power supply has not been working, 12V has not been established, and the q814 base level is pulled low and error protection. After the replacement of C870, troubleshooting.

[cases of 2] fault phenomenon on standby indicator does not light, no light no sound without "squeak".

Analysis and maintenance of the boot, the fuse, R841 open circuit, C817 breakdown. After replacing fuses, C817 and R841, no obvious short circuit faults of 300V and 113V are found. Voltage regulator with power supply and power of the test, the city from 120V to 240V can be normal to watch, but can not remote control, standby indicator is still not bright. Check the auxiliary power supply, and found that Q810, D810, Q813, D811, D813 have been damaged. After all these devices are replaced, troubleshooting.

[3] malfunction indicator light does not shine, "three".

Analysis and maintenance of teardown inspection, fuse, R841 burning, output tube breakdown. With the isolation voltage regulator power supply and the false load test machine, it is found that the output voltage increases with the increase of the supply voltage. Stop check, IC801 internal Q3 has been breakdown. Because the local purchase to, try to disconnect the IC801 3 feet, in the cooling of the original piece on another installation a high-power switch tube 2SC411, instead of Q3, the very C connected to P2, B pole connected foot of IC801 II, e pole is connected IC801 4 feet. Restart, everything is normal.

Substitution should note the following: (1) the original IC801 internal Q3 emitter and voltage stabilizing circuit must be in good condition. (2) substitution switch should meet the following requirements: BVCBO = 1500V, PCM = 100W, ICM = 7A. In the same way, the same 2SD1403 (for 21 inch TV switch tube) is used for the same kind of tube.

If you can buy to STR50213, also can substitute, but due to lack of power, substitution, can be in the 2, 3, 4 feet (Q3) outreach a power switch tube (such as 2SD1403 2SC1942), and pay attention to insulation.